The invention relates to electronic semiconductor devices, and, more particularly, to antireflective structures and fabrication methods for such structures.
Semiconductor integrated circuits with high device density require minimal size structures such as short gates for field effect transistors, small area emitters for bipolar transistors, and narrow interconnects between devices. The formation of such polysilicon or metal (or a stack of metals or a metal silicide on polysilicon) structures typically involves definition of the locations of such structures in a layer of photoresist on a layer of polysilicon or metal by exposure of the photoresist with radiation passing through a reticle containing the desired structure pattern. During the exposure, radiation reflected from the underlying material (e.g., polysilicon, metal, . . . ) can degrade the pattern developed in the photoresist, so include an antireflective coating or layer on the polysilicon or metal. Commercial antireflective coatings include organic materials and TiN which strongly absorb at the radiation wavelength, such as polymers with dye-groups for absorption.
After exposure and development of the photoresist, the underlying layers of antireflective coating plus material (polysilicon, metal, . . . ) are anisotropically etched using the patterned photoresist as the etch mask (or the antireflective coating may first be wet developed and then the underlying material anisotropically etched). Thus the minimal structural linewidth equals the minimal linewidth that can be developed in the photoresist.
One approach to overcome the linewidth limitation patterns photoresist and then isotropically etches the patterned photoresist to shrink its size and thereby emulate a smaller original linewidth. However, this approach has a problem of the isotropic etch of the patterned photoresist also etches the antireflective coating. Ogawa et al, 2197 Proc. SPIE 722 (1994) describes the use of silicon oxynitride as an antireflective coating on a oxide coated tungsten silicide layer and on an aluminum layer for i-line and deep ultraviolet radiation by quarter-wavelength thickness for reflective interference.